It is known to dye petroleum fuels as a means of visual identification, e.g., for tax purposes, identity of source, to guard against mixing of grades, etc. The dyes used to color petroleum dyes are generally of the type designated "solvent dyes".
An alternative to petroleum fuel is ethanol, currently widely used in Brazil. There are advantages to using dyes currently used in petroleum fuels as dyes in ethanol. In particular, such dyes have been tested and used extensively in internal combustion engines and are known to be compatible for use in internal combustion engines.
Unfortunately, as ethanol is much more polar than petroleum fuels, certain solvent dyes commonly used in petroleum fuels have very low solubility in ethanol. In the ethanol fuel itself, very little ethanol-solubility is required as dyes of this type are typically added in the parts per million ranges, e.g. 1-100 ppm. However, for a dye to be used in practice, it must generally be available in a concentrated form to avoid the necessity of storing, shipping and handling large volumes, and must generally be available in liquid form for accurate metering into the fuel. When a dye is very insoluble in ethanol, it is difficult to supply as a concentrate to ethanol as the concentrate will tend to separate from the dye.
The present invention is directed to a method of introducing particular solvent dyes having very low ethanol-solubility into ethanol.